Abnormal bleeding from being on birth control?

I started taking the generic brand of Yasmin several weeks ago, i only took it for about a week and then stopped taking it. Now, i woke up this morning and i was bleeding I am not suppose to have my period for at least another 15 days I just got done having my period. I don't know what could be wrong . I have always had a normal period and gotten it around the time i am suppose to. Last time i had my period was on the 23rd of August and now i am bleeding again..